Method for producing foamed-in-mold product of aromatic polyester based resin

ABSTRACT

The present invention provides a process for producing a molded foam article of a crystalline aromatic polyester resin. The process is characterized by heating the surface temperature of a mold for cavity-molding to the temperature within a range of from (td+35) to (Tg+57)°C. (Tg is a glass transition temperature of the crystalline aromatic polyester resin prepuffs), thereby to mold prepuffs, and cooling the surface of the mold to a temperature not lowered than Tg for at least 20 seconds.

TECHNICAL FIELD

The present invention relates to a process for producing a molded foamarticle of a crystalline aromatic polyester resin and, moreparticularly, to a process for producing a molded foam article used inindustrial parts, food containers or the like, which is superior invarious characteristics such as low density and heat resistance and hasa good appearance.

BACKGROUND OF THE INVENTION

An aromatic polyester resin represented by a polyethylene terephthalatehas widely been used in the fields of electric/electronic parts,automotive parts, industrial parts, and packagings such as film andbottle containers because of its comparatively low price, excellentchemical properties such as chemical resistance, solvent resistance andweathering resistance, and physical properties such as heat resistance,rigidity and gas-barrier property. Therefore, trials to produce a moldedfoam article containing an aromatic polyester resin as a base resin,which is lightweight and has excellent insulating properties andcushioning properties, have been made. For example, Publication ofUnexamined Patent Application No. JP 51-50365, A (1976) discloses apotentially foamable polyester fiber produced by impregnating anunstretched fiber, which is obtained by wet spinning or dry spinning ofa high-melting point polyester, with a low-boiling point liquid which isinsoluble or slightly soluble in the polyester. This publication alsodiscloses that a polyester foam was obtained by heating the potentiallyfoamable polyester fiber to the temperature higher than its plasticationtemperature. Publication of Unexamined Patent Application No. JP59-135237, A (1984) discloses a foamed linear polyester resin, and alsodiscloses that a food container capable of being heated in an oven canbe obtained by forming a sheet of the foamed resin.

However, an object of the former publication is to finally obtain athread-like foam by spinning a polyester to form a thread-like product,impregnating the product with a low-boiling point liquid as a blowingagent, and dipping in an oil bath, thereby to foam the product.Therefore, the former publication does not suggest a technical idea ofprocessing the thread-like foam again to mold a molded foam articleother than the thread-like product itself. The latter publicationdiscloses that a foamed sheet is produced by treating a blend of alinear polyester/polycarbonate at high temperature and conductingextrusion foaming of the blend using carbon dioxide released frompolycarbonate as a blowing agent to produce a foamed sheet. Only sheetshaving a density of 0.83 g/cm³ are described in the Examples of thepublication. Therefore, a foam having a lower density is hardlyobtained.

In Publication of Unexamined Patent Application No. JP 2-251543, A(1990), the present applicant has already suggested a process forproducing a low density foamed sheet in an industrial manner, and hassucceeded in practical application. As a result, it became possible toform the sheet into a lightweight container having a desired shape by aprocess such as vacuum forming and matched-mold forming using such alow-density foamed sheet.

As described above, various studies of thermally forming a foamed sheetproduced by extrusion foaming to obtain a container such as food trayhave been made. However, a so-called cavity-molding process of aromaticpolyester resin prepuffs using a mold, followed by cooling and furtherremoval from the mold to obtain a molded foam article having anarbitrary shape wherein the prepuffs are expanded and fused has neverbeen studied sufficiently. The present applicant also has studiedintensively about this process.

To obtain a molded foam article of a polystyrene resin by thecavity-molding process, the molded foam article is produced through thestep of impregnating resin particles with a blowing agent, pre-expandingthe resin particles so impregnated (so called prepuffs), andcavity-molding(expanding and fusing) the prepuffs. However, in casewhere these steps are applied to a polyester resin, a long time isrequired in the step of impregnating with the blowing agent orimpregnation is not conducted because the polyester resin is superior ingas-barrier property. The crystallinity of the prepuffs is excessivelyhigh by heating on impregnation and pre-expanding and the prepuffs arenot fused each other on cavity-molding and, therefore, a molded foamarticle is not obtained.

Thus, the present applicant has found that the crystallinity of prepuffscan be set to 25% or less by employing the step of melt-kneading apolyester resin and a blowing agent, conducting extrusion foaming of themixture using an extruder, and cutting the resulting foamed extrudate togive prepuffs and that the prepuffs are expanded and fused each other bycavity-molding to obtain the desired molded foam article {Publication ofUnexamined Patent Application No. JP, 8-174590, A (1996)}.

This molded foam article is free from gaps between prepuffs and has auseful heat resistance.

However, prepuffs made of a general purpose polyester resin having acrystallization peak temperature lower than 130° C. is used in thismolded foam article and, therefore, the crystallization rate isconsidered very fast. Therefore, the fusion rate is improved bycontrolling the crystallinity of the prepuffs to 25% or less, therebymaking it possible to provide a molded foam article by fusing theprepuffs each other to some extent. However, the fusion ratio ofprepuffs is 20% at most and a molded foam article having sufficientfusion ratio such as 30% or more could not be obtained.

Since the crystallinity of the molded foam article could be enhanced to20% or more, the heat resistance can be imparted. However, since thefusion ratio is insufficient, the dimensional change on heating at 140°C. for 24 hours is at least about 2.5% and could not be controlled to 2%or less.

Recently, a molded foam article whose dimensional change on heating at140° C. for 24 hours is controlled to 2% or less, preferably 1% or less,has been required for applications such as industrial parts andautomotive parts, however the molded foam article could not respond tothese requirements.

On the other hand, when the crystallization rate of a polyester resin isinhibited, for example, when the crystallization peak temperature isadjusted to 130-180° C., the crystallinity of prepuffs can be reduced to8% or less. Since the crystallinity is inhibited, proceeding of thecrystallinity on cavity-molding can also be inhibited and the fusion ofthe prepuffs can be improved to excellent fusion ratio of not less than40%.

When the crystallization rate is inhibited, the fusion can be improved.However, in case where the molded foam article is produced by a generalprocess for cooling immediately after the completion of molding,removing the molded foam article from the mold, so-called sink whereinthe center portion of the molded foam article shrinks immediately afterremoval from the mold, which is considered to be caused by lowcrystallinity of the molded foam article, occurs and the mature step ofaging until sink is restored is required.

This sink is a phenomenon wherein the thickness of the plate-like moldedfoam article varies from the side portion to the center portion and thecenter portion is thin. This phenomenon is particularly remarkable inthe prepuffs wherein the crystallization rate was inhibited. Therefore,even if the molded temperature is raised or the mold time is prolonged,to thereby to accelerate crystallization and to inhibit sink, melt marksare formed on the surface of the molded foam article, resulting in poorappearance. Therefore, it is difficult to produce a good molded foamarticle.

Accordingly, a mature period for several weeks until sink is restoredafter the production of the molded foam article of the aromaticpolyester resin is required. Therefore, the mature period and place formaturing can cause an increase in cost.

If the above-described problems are solved, it is expected that themolded foam article of the aromatic polyester resin finds its way into avariety of applications such as building materials, constructionmaterials, industrial members, automotive parts, etc., as a more highlyfunctional material than that of conventional polystyrene or polyolefinproducts taking advantage of the excellent characteristics describedabove.

OBJECTS OF THE INVENTION

An object of the present invention is to provide a process for producinga molded foam article, which has sufficient fusion ratio such as about30% or more and excellent dimensional stability capable of inhibitingthe dimensional change ratio on heating, even in case of using prepuffsof the general purpose polyester resin. Such a molded foam article canbe suitably used in applications such as industrial parts and automotiveparts.

In this invention, in the case where cavity-molding is conducted byusing prepuffs wherein the crystallization rate is inhibited, forexample, the crystallization peak temperature is adjusted to within arange of from 130 to 180° C., a molded foam article of an aromaticpolyester resin can be produced wherein generation of sink, that isliable to occur in the molded foam article, is also inhibited.

Another object of the present invention is to provide a process forproducing a molded foam article, wherein the above fusion, sink andappearance are improved and the heat resistance is imparted byaccelerating the crystallinity within a shorter time, by adding a stepof heating again to a specific temperature after the step of immediatelyfollowing the molding.

DISCLOSURE OF THE INVENTION

The present invention relates to a process for producing a crystallinearomatic polyester resin molded foam article, which comprises moldingcrystalline aromatic polyester resin prepuffs using male and female moldmembers of a mold assembly through the following steps (1) to (4):

step (1) of filling a mold cavity, which is formed by closing the maleand female mold members, with the crystalline aromatic polyester resinprepuffs;

step (2) of heating a surface of the mold to a temperature in a range offrom (Tg+35) to (Tg+57)°C. (Tg is a glass transition temperature of thecrystalline aromatic polyester resin prepuffs), thereby to mold thefilled prepuffs;

step (3) of cooling the surface of the mold to a temperature not lowerthan Tg over a period of at least 20 seconds while holding the moldedfoam article in the mold as it is; and

step (4) of removing the molded foam article from the mold, afterfinally cooling the surface of the mold lower than Tg.

According to the process for the present invention, by providing step(3) of cooling the molded foam article to the temperature at which thesurface temperature of the mold for cavity-molding is not lower than Tgfor a period of 20 seconds or more without removing from the mold afterthe completion of heating for cavity-molding (expanding and fusing), amolded foam article having a sufficient fusion ratio of about 30% ormore can be produced even when using prepuffs having very highcrystallization rate equivalent to that of a general purpose polyesterresin. The molded foam article whose fusion ratio was improved to 30% ormore can satisfy the quality standard wherein the thermal dimensionalchange on heating at 140° C. for 24 hours is lowered to 2% or less,which has been required in applications such as industrial members andautomotive members.

The present invention also relates to a process employing the step ofcooling once under the above-described specific conditions, there can beproduced a molded foam article having a good appearance whereingeneration of sink which is liable to occur in the molded foam articleis also inhibited in case of molding prepuffs wherein thecrystallization rate is inhibited, for example, the crystallization peaktemperature is adjusted to within a range of from 130 to 180° C.

In the process for producing a crystalline aromatic polyester resinmolded foam article of the present invention, the addition of followingstep (3a) between steps (3) and (4) is effective:

step (3a) of heating the surface of the mold again to the temperaturewithin a range of from (Tg+20) to (Tg+57)°C., acceleratingcrystallization of the molded foam.

The better process of the present invention, wherein the cooling of step(3) is conducted for a shorter time, for example from 20 to 300 secondsand the providing of the above step (3a) between the steps (3) and (4),the before described fusion is further improved and generation of sinkis inhibited. At the same time, crystallization is accelerated within ashorter time, thereby making it possible to impart the heat resistanceto the molded foam article having good appearance.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view showing one embodiment of a mold forcavity-molding used for carrying out the process for producing themolded foam article of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The process for producing a molded foam article of the present inventionwill be described in detail below with reference to FIG. 1.

A mold for cavity-molding is equipped with male mold member 1 and femalemold member 2 of a mold assembly, which form a mold cavity Ccorresponding to the shape (shape of plate in the figure) of the moldedfoam article when the mold is closed as shown in FIG. 1.

The male mold member 1 and female mold member 2 are respectively formedin a hollow shape equipped with spaces 10, for introducing steamtherein. Each mold member has certain specific piping connect to it.Steam pipes 31, 41 are provided for supplying steam supplied from asupply source (not shown) of steam, the steam pipes being provided withsteam valves 31 a, 41 a along the line. Drain pipes 32, 42 are providedfor draining steam out of the spaces 10, 20, said drain pipes beingprovided with drain valves 32 a, 42 a along the line. Exhaust pipes 33,43 are provided for exhausting the spaces 10, 20 on filling of a moldcavity C with prepuffs or exhausting the spaces 10, 20 for pressurecontrol on molding, said exhaust pipes being provided with exhaustvalves 33 a, 43 a along the line. Pressure reducing pipes 34, 44 areprovided for reducing a pressure in the spaces 10, 20, said pressurereducing pipes being provided with pressure reducing valves 34 a, 44 aalong the line.

Steam supplied into the spaces 10, 20 of the male mold member 1 andfemale mold member 2 through the steam pipes 31, 41 is supplied into themold cavity C through many fine vent holes 11, 21 formed on the moldsurface constituting the mold cavity C of the male mold member 1 andfemale mold member 2, the steam is thus used for cavity-molding theprepuffs with which the mold cavity C is filled. As a heating medium,for example, a hot air can be used, in addition to steam, but steam ismost effective to mold effectively.

In the spaces 10, 20 of the male mold member 1 and female mold member 2,cooling pipes 5, 6 are provide having plural cooling water nozzles 51,61, which are used for supplying cooling water for cooling the moldedfoam article after cavity-molding both by contacting the mold backsurface constituting the cavity C, and by flowing into the mold cavity Cthrough the vent holes 11, 21.

The female mold member 2 as the cavity side is provided with a fillinggun 7 for supplying prepuffs into the mold cavity C and eject pins 8,8for extruding the molded foam article after cavity-molding from the moldcavity C on opening of the male mold member 1 as the movable side. Inthe drawing, reference numerals 81, 81 denote springs for retaining theeject pins 8, 8 in the state shown in the figure on closing of the mold.

To carry out the process for producing the molded foam article of thepresent invention using the above mold for cavity-molding, a mold cavityC is filled with a predetermined amount of prepuffs of a crystallinearomatic polyester resin using the filling gun 7 with the above malemold member 1 and female mold member 2 together, steam valves 31 a, 41a, drain valves 32 a, 42 a and pressure reducing valves 34 a, 44 a areclosed and exhaust valves 33 a, 43 a are opened. This enables exhaustionof the spaces 10, 20 as well as the mold cavity C through exhaust pipes33, 34 {step (1)}.

The exhaust valves 33 a, 43 a are closed and steam valves 41 a and drainvalve 32 a are opened. Then steam under low pressure (e.g. about 0.01 to0.05 MPa in gauge pressure) is supplied (one side heating) from the sideof the female mold member 2 into the mold cavity C for a predeterminedtime. The steam valve 41 a and drain valve 32 a are closed and the steamvalve 31 a and drain valve 42 a are opened. Then steam under the samelow pressure (e.g. about 0.01 to 0.05 MPa in gauge pressure) is supplied(another side heating) from the side of the male mold member 1 into themold cavity C for a predetermined time.

One side heating and another side heating are carried out to remove airwhich is present between the prepuffs with which the mold cavity C isfilled. This may be optionally carried out after or with reducing of thepressure in the mold cavity C by opening the pressure reducing valves 34a, 44 a. The one side heating and another side heating are pretreatmentsto be carried out before-heating for cavity-molding as described below.

The steam valves 31 a, 41 a are opened and all of the other valves areclosed. Then, steam at high pressure (e.g. about 0.02 to 0.10 MPa ingauge pressure) is supplied into the mold cavity C for a predeterminedtime and the mold is heated so that the surface temperature of the moldportion in contact with the prepuffs are within a range of from (Tg+35)to (Tg+57)°C., thereby to expand and to fuse the prepuffs each other(cavity-molding) {step (2)}.

In this case, the exhaust valves 33 a, 43 a may be open or closed toadjust the pressure so that the mold surface temperature isapproximately fixed.

When the mold surface temperature is lower than (Tg+35)°C., sufficientcavity-molding of the prepuffs does not occur even if steam iscontinuously introduced for a long time. Extension of the surface of themolded foam article becomes poor and gaps between the prepuffs increase,resulting in a poor molded foam article.

On the other hand, when the mold surface temperature on heating ishigher than (Tg+57)°C., the surface of the molded foam article is liableto be molten, resulting in a poor molded foam article.

In this specification, a pore which does not pass through one of themold members from the back surface (side of spaces 10, 20) to themolding surface is formed at the portion facing to the mold cavity C inat least one of the male mold member 1 and female mold member 2. Atemperature sensor, such as a thermocouple 100, was inserted and wasfixed into the pore. The measured temperature was taken as a moldsurface temperature. The distance from a tip of the sensor to the actualsurface of the mold is approximately 1 to 3 mm but since the mold ismade of a metal having good thermal conductivity, a difference intemperature between them and a difference in time with the change of thetemperature may be neglected.

To maintain a good appearance of the molded foam article, the timerequired for cavity-molding can be reduced when the temperature becomeshigher than within the above range of from (Tg+35) to (Tg+57)°C.However, the time required for cavity-molding is prolonged when thetemperature becomes lower. The heating time and heating temperature varydepending on the shape of the mold, and the thickness and density of themolded foam article, but the heating time is preferably from about 5seconds to 3 minutes.

After the completion of heating for cavity-molding, the surface of themold is cooled to the temperature not lower than Tg for a period of 20seconds or more while holding the molded foam article in the mold as itis {step (3)}.

By this cooling step, a molded foam article having sufficient fusionratio of not less than 30% can be produced even when using prepuffs ofthe general purpose polyester resin. The molded foam article whosefusion ratio was improved to 30% or more can satisfy the qualitystandard wherein the thermal dimensional change ratio on heating at 140°C. for 24 hours is lowered to 2% or less. This quality standard has beenrequired in applications such as industrial members and automotivemembers.

There can be produced a molded foam article having a good appearancewherein generation of sink is also inhibited in case of cavity-moldingprepuffs wherein crystallization rate is inhibited, for example, thecrystallization peak temperature is adjusted to within a range of from130 to 180° C.

In case where the time of step (3) is 20 seconds or less, that is, themold surface temperature is rapidly cooled to Tg or less within 20seconds, the above-described effect can not be obtained. Enough coolingtime in the above step is about 900 seconds or less. Even if the coolingtime is longer than 900 seconds, there can not be obtained furthermerits warranting prolonging a cavity-molding cycle.

The specific cooling process is preferably gentle air cooling ofallowing the assembly to stand in the state where all of theabove-described steam valves 31 a, 41 a, drain valves 32 a, 42 a, theexhaust valves 33 a, 43 a and pressure reducing valves 34, 44 are closedafter the completion of the cavity-molding. During the air cooling, themold surface temperature is slowly lowered, but the crystallization ofthe molded foam article can be accelerated.

For the purpose of slowing the reduction of mold surface temperatureduring this cooling, steam can also be introduced. The temperature ofsteam to be introduced is preferably set to the temperature which is 2°C. or more, particularly 4° C. or more, lower than the cavity-moldingtemperature. The time required for introducing steam may beappropriately set according to the shape of the mold, thickness anddensity of molded foam article. Steam may be introduced continuously orintermittently.

Only when the cooling step after the completion of cavity-molding isconducted for the above-described relatively long time, thecrystallization of the molded foam article is sufficiently accelerated,thereby making it possible to impart the desired heat resistance.

To increase the crystallinity efficiently within a shorter time, forexample, the crystallization of the resin is preferably accelerated byre-heating the assembly for 10 to 180 seconds so that the mold surfacetemperature is in a range of from (Tg+20) to (Tg+57)°C. after adjustingthe time of the cooling step to at least 300 seconds {step (3a)}.

Since the crystallinity of the molded foam article is improved in theabove step (3), it is possible to inhibit the surface from melting byre-heating using a temperature within the temperature range of the step(3a). When the re-heating time is less than 10 seconds, the effect ofaccelerating the crystallization becomes poor. When the re-heating timedoes not exceed 180 seconds, a reduction in cavity-molding cycle time isremarkable.

The conditions of re-heating are set according to the density orthickness of the molded foam article, but the above temperature rangecausing no melting on the surface of the molded foam article ispreferred. That is, the conditions wherein the mold surface temperaturedoes not exceed (Tg+57)°C. are preferred. When the mold surfacetemperature exceeds this temperature, the surface of the molded foamarticle is liable to be molten, which is not preferred. Thecrystallization is preferably accelerated under homeothermal conditions.

When the mold surface temperature on re-heating is less than (Tg+20)°C.,the crystallization rate is late and is not put to practical use.

After the completion of the cavity-molding, cooled under predeterminedconditions and re-heated if necessary, the mold surface temperature isfinally cooled to Tg or less by water cooling by the supply of coolingwater through cooling water nozzles 51, 61 of the cooling pipes 5,6.After removing the molded foam article from the mold, an excellentmolded foam article can be produced.

As the prepuffs of the crystalline aromatic polyester resin used in theprocess for the present invention, especially, those having acrystallization peak temperature of 130 to 180° C. are preferably used,in addition to a general purpose PET resin.

Since the crystallization peak temperature means the temperature atwhich the crystallinity becomes maximum by heating, the higher the peaktemperature, the lower the crystallization rate. Prepuffs made of thegeneral purpose PET have a crystallization peak temperature of not morethan 130° C. and have a very fast crystallization rate. On the otherhand, prepuffs having a crystallization peak temperature of not lessthan 130° C. have a late crystallization rate than that of the prepuffsmade of the general purpose PET, thereby making it possible to limit thecrystallinity within lower range than before and to inhibit thecrystallization from proceeding in the cavity-molding step. Therefore,the fusion between the prepuffs on cavity-molding is further improved toset the thermal dimensional change on heating at 140° C. for 24 hours tobe lowered to 2.0% or less, thereby making it possible to produce amolded foam article having excellent appearance and mechanical strength.

Prepuffs having a crystallization peak temperature of higher than 180°C. can not impart the desired heat resistance to the molded foam articlebecause its crystallization rate is too late and the article hardlycrystallizes. In addition, the range of the cavity-molding conditionsbecomes narrow, thereby making it difficult to conduct cavity-molding.Alternatively, since an increase in the crystallinity is excessivelylow, the molded foam article can not stand against a heating medium suchas steam and shrinkage of the surface occurs. Therefore, a molded foamarticle having good appearance is not obtained.

The crystallization peak temperature was measured by using adifferential scanning calorimetry (DSC) in accordance with the measuringprocedure defined in the Japanese Industrial Standard No. JIS K7121₋₁₉₈₇“Testing Method for Transition Temperatures of Plastics”.

Specifically, a predetermined amount of prepuffs is set in a measuringcontainer of DSC and heated to 280° C. at a heating rate of 10° C./minand, after maintaining at the same temperature (280° C.) for 10 minutes,the sample is left to cooled to room temperature (23° C.). Thereafter,the crystallization peak temperature is measured by heating the sampleagain at a heating rate of 10° C./min.

In order to control the crystallization peak temperature of the prepuffswithin the above range, the crystalline aromatic polyester resinconstituting the prepuff should be modified by changing the element ofdicarboxylic acid and/or diol.

Specifically, isophthalic acid represented by the formula (1):

can be used as dicarboxylic acid, or 1,4-cyclohexanedimethanolrepresented by the formula (2):

can be used as diol, which may be used either singly or combination. Thetotal content of a unit derived from isophthalic acid (hereinafterreferred as IPA unit) and/or a unit derived from1,4-cyclohexanedimethanol (hereinafter referred as CHDM unit) in thecrystalline aromatic polyester resin should be within a range of from0.5 to 10% by weight.

To markedly improve the fusion between the prepuffs, the content of theIPA unit and/or CHDM unit should be preferably from about 0.6 to 9.0% byweight, and more preferably from about 0.7 to 0.8% by weight.

Among other components constituting the crystalline aromatic polyesterresin of the present invention, can include as dicarboxylic acid forexample, terephthalic acid and phthalic acid, in addition to isophthalicacid and 1,4-cyclohexanedimethanol.

The diol component of the present invention can include, for example,ethylene glycol, α-butylene glycol (1,2-butanediol), β-butylene glycol(1,3-butanediol), tetramethylene glycol (1,4-butanediol), 2,3-butyleneglycol (2,3-butanediol), neopentyl glycol or the like.

The material for crystalline aromatic polyester resin may contain asmall amount of a polyhydric (tri- or polyhydric) carboxylic acid or ananhydride thereof as an acid component (e.g. tricarboxylic acid such astrimellitic acid, tetracarboxylic acid such as pyromellitic acid, etc.)and a polyhydric (tri- or polyhydric) alcohol as an alcohol component(e.g. triol such as glycerin, tetraol such as pentaerythritol, etc.), inaddition to the respective components described above, in such mannerthat the crystallization peak temperature of the crystalline aromaticpolyester resin does not deviate from the range of from 130 to 180° C.

The crystalline aromatic polyester resin used in the present inventionis produced by the polycondensation reaction, in such manner that thetotal content of the IPA unit and/or CHDM unit is within a range of from0.5 to 10% by weight of the crystalline aromatic polyester resin.

In the present invention, the following additives can be added to thecrystalline aromatic polyester resin.

The additive can include, for example, flame retardants, antistaticagents, pigments, expansion nucleating agents, melt tension modifiers,antioxidants, etc., in addition to blowing agents.

As the blowing agent, any of chemical and physical blowing agents can beused.

The chemical blowing agent, which is decomposed at the temperaturehigher than the softening point of the crystalline aromatic polyesterresin, can include azodicarbonamide, dinitropentamethylenetetramine,hydrazoldicarbonamide, sodium bicarbonate or the like.

The physical blowing agent can include, for example, saturatedhydrocarbon such as propane, n-butane, isobutane, n-pentane, isopentane,cycropentane, hexane, etc.; halogenated hydrocarbon such as methylchloride, Freon®, etc.; and an ether compound such as dimethyl ether,methyl-tert-butyl ether, etc.

Furthermore, an inorganic gas such as carbon dioxide, nitrogen or thelike can be used as the blowing agent.

As an expansion nucleating agent, for example, a polytetrafluoroethyleneresin is preferred.

In the present invention, there can be added polyolefin resin such aspolypropylene resin, thermoplastic elastomer resin such as polyesterelastomer resin, polycarbonate resin, ionomer resin or the like to thecrystalline aromatic polyester resin as far as a large influence is notexerted on the crystallinity or crystallization rate.

As an melt tension modifier, for example, epoxy compound such asglycidyl phthalate, acid anhydride such as pyromellitic dianhydride, andmetal compound of the group Ia and IIa such as sodium carbonate can beused alone or in combination.

The prepuffs are produced by extrusion foaming the crystalline aromaticpolyester resin and cutting the resulting foamed extrudate (foam) intoparticles.

As described above, the step of impregnating the crystalline aromaticpolyester resin with the blowing agent is eliminated thereby to save thetime, cost and labor and, at the same time, the crystallinity of theprepuffs is further lowered, thereby making it possible to improve thefusion between the prepuffs on cavity-molding.

The size of the prepuffs thus produced is preferably from about 0.5 to 5mm in an average particle diameter.

The crystallinity (%) was determined from a quantity of heat of coldcrystallization and a quantity of heat of fusion, that were measured inaccordance with the measuring procedure defined in the JapaneseIndustrial Standard No. JIS K7121₋₁₉₈₇ using a differential scanningcalorimetry (DSC) in the same manner as in measurement of thecrystallization peak temperature described previously, by the followingequation: ${{Crystallinity}\quad (\%)} = {\frac{\begin{matrix}\left( {{Quality}\quad {of}} \right. \\\begin{matrix}{{heat}\quad {of}\quad {fusion}} \\\left. {{per}\quad {mol}} \right)\end{matrix}\end{matrix} - \begin{matrix}\left( {{Quantity}\quad {of}\quad {heat}\quad {of}} \right. \\\begin{matrix}{{cold}\quad {crystallizsation}} \\\left. {{per}\quad {mol}} \right)\end{matrix}\end{matrix}}{\begin{matrix}\left( {{Quantity}\quad {of}\quad {heat}\quad {of}\quad {fusion}\quad {per}\quad {mol}} \right. \\\left. {{of}\quad {perfect}\quad {crystallized}\quad {PET}\quad {resin}} \right)\end{matrix}} \times 100}$

The quantity of heat of fusion per mol of the perfect crystallized PETresin in the equation was set to 26.9 kJ due to the description ofPolymer Data Handbook (issued by Baifukan).

Specifically, a predetermined amount of the prepuffs as a samplemeasured was set in a measuring container of DSC and the quantity ofheat of cold crystallization and quantity of heat of fusion weremeasured with heating at a heating rate of 10° C./min. The crystallinityof the prepuffs was determined from the measurement results on the basisof the above equation.

In the present invention, the bulk density of the prepuffs arecontrolled within a range of from 0.01 to 1.0 g/cm³ so as to obtain amolded foam article which is lightweight and is superior in mechanicalstrength, heat resistance, insulating properties, cushioning propertiesand chemical resistance.

The bulk density of the prepuffs are preferably from about 0.03 to 0.8g/cm³, and more preferably from about 0.04 to 0.6 g/cm³, within theabove range.

To produce a further lightweight molded foam article, the bulk densityof the prepuffs are particularly preferably not more than 0.1 g/cm³,within the range of from 0.01 to 1.0 g/cm³.

In case where prepuffs having a comparatively low bulk density of notmore than 0.1 g/cm² are produced, there should be used a process forimpregnating the prepuffs produced by the previously described processwith a gas under pressure and subjecting the impregnated prepuffs to thestep of re-expanding by heating, thereby to control the bulk density toa lower value. The re-expanding step may be repeated twice or more.

In the re-expanding step, the gas with which the prepuffs areimpregnated can include nitrogen, air, carbon dioxide gas, helium,methane, ethane, propane, butane or the like.

Among them, an inorganic gas is preferred and an air is particularlypreferred. Among the inorganic gases, an air containing a large amountof nitrogen is advantageous in that it is not rapidly dissipated likecarbon dioxide gas when the prepuffs are re-expanded. Re-expanding canbe sufficiently conducted at low temperature within a short time underthe conditions of a heating temperature of 55 to 90° C. and a heatingtime of 12 minutes or less, that have never been considered. Therefore,a rise in the crystallinity of the prepuffs are inhibited, therebymaking it possible to improve the foaming and fusion on cavity-moldingand to improve the mechanical strength.

In the vapor phase impregnation for impregnating the prepuffs with theabove gas, the impregnation pressure is preferably from about 0.1 to 5MPa, and particularly from about 0.2 to 2 MPa, in gauge pressure. Theimpregnation time is preferably from about 1 to 24 hours, andparticularly from about 1 to 12 hours. The temperature is preferably Tgor less.

In case where the prepuffs impregnated with the gas are re-expanded, forexample, hot air, hot water, steam, hot oil, hot gas, etc. can be usedas a heating medium. In view of good handling of the prepuffs afterre-expanding and efficiency of re-expanding, hot air or steam ispreferred.

The re-expanding step is suited for production of prepuffs having a bulkdensity of not more than 0.1 g/cm³ (referred to as “secondaryprepuffs”). Accordingly, even in case where the bulk density of theprepuffs before re-expanding (referred to as “primary prepuffs”) ishigher than 0.1 g/cm³, the bulk density can be controlled lower bycarrying out the re-expanding step.

The prepuffs may be in the shape of a general cylinder, square or chip.Among them, a generally cylindrical shape is particularly preferred.This reason is as follows. That is, in case of cavity-molding, the moldcavity formed by closing the mold for cavity-molding equipped with maleand female mold members of the mold assembly previously described can befilled with the prepuffs more evenness. The molded foam article producedthe prepuffs can exhibit excellent mechanical strength.

An open cell ratio of the prepuffs (primary prepuffs/secondary prepuffs)is preferably from 5 to 35%.

When the open cell ratio of the prepuffs exceeds 35%, a harmfulinfluence is exerted on cavity-molding, sometimes, and there is a fearthat good molded foam article can not be produced.

On the other hand, when the open cell ratio is not more than 5%, thereis a fear that shrinkage of a molded foam article on removal from themold increased. To the contrary, when using the prepuffs having an opencell ratio within a range of from 5 to 35%, shrinkage on removal fromthe mold can be inhibited and the appearance does not become poor due togeneration of wrinkles on the surface of the molded foam article.Accordingly, this open cell ratio is particularly suited for use asindustrial parts to which high dimensional accuracy is required.

The prepuffs impregnated previously with inorganic gases such as air,carbon dioxide gas, nitrogen, helium and the like can increase anexpansion force on cavity-molding, and a good molded foam article can beobtained.

Among these inorganic gases, air containing a large amount of nitrogenis particularly preferred. The pressure on impregnating with theinorganic gas is preferably from 0.01 to 5 MPa at gauge pressure, andmore preferably from 0.02 to 2 MPa at gauge pressure.

Regarding the molded foam article produced by the process for thepresent invention, the molded foam article having a sufficient fusionratio of about not less than 30% can be obtained from prepuffs using ageneral purpose polyester resin. Since the crystallinity of the moldedfoam article can be improved to 20% or more, the molded foam article cansatisfy the quality wherein the thermal dimensional change ratio onheating at 140° C. for 24 hours is lowered to 2% or less, which has beenrequired in applications such as industrial members and automotivemembers.

When using prepuffs wherein crystallization rate of the polyester resinwas inhibited, for example, the crystallization peak temperature wasadjusted within a range of from 130 to 180° C., the fusion ratio can beimproved to 40% or more, and to 60% or more. In case of those whereinthe crystallinity of the molded foam article was increased to 20% ormore by the relatively long cooling time due to the step (3) orre-heating due to the step (3a), the above thermal dimensional changeratio can be improved to 2% or less, and to 1% or less.

In the molded foam article using prepuffs whose crystallization rate wasinhibited, there can be produced a molded foam article having goodappearance wherein generation of sink which is liable to occur in themolded foam article is also inhibited even in case where thecrystallinity is not increased to 20% or more as described above.

Accordingly, a molded foam article of a crystalline aromatic polyesterresin, which is superior in appearance and mechanical strength such asbending strength, can be produced by using prepuffs made of a generalpurpose polyester resins or prepuffs whose crystallization rate wasinhibited.

The molded foam article can be reused after being used in variousapplications. By reusing the used molded foam article, it is madepossible to contribute to effective reuse of resources and reduction indust and to reduce the cost of the molded foam article.

As described above in detail, according to the present invention, thereis exerted such specific operation/working-effect that a good moldedfoam article, which has excellent appearance, improved fusion betweenthe prepuffs and excellent mechanical strength, can be produced in aneasy and efficient manner.

EXAMPLES

Advantages of the present invention will be described in detail by thefollowing Examples and Comparative Examples.

Any of the following measurements was conducted under an measuringenvironment of a temperature of 23° C.±2° C. and a humidity of 50±5%RHin accordance with the Japanese Industrial Standard No. JIS K7100₋₁₉₈₁“Standard Atmospheres for Conditioning and Testing of Plastics”.

The crystallization peak temperature of the prepuffs, and thecrystallinity of the prepuffs, molded foam article and the like weredetermined from the results measured in accordance with the measuringprocedure defined in the Japanese Industrial Standard No. JISK7121₋₁₉₈₇, as described above.

The content of the IPA unit and/or CHDM unit in the crystalline aromaticpolyester resin, and the melt tension of the resin were measured by thefollowing procedures, respectively. Measurement of content of IPA unit.

After weighing about 100 mg of a sample in a pressure-resistant tefloncup, 10 ml of dimethyl sulfoxide for absorption spectrochemical analysismanufactured by Wako Pure Chemical Industries, Ltd. and 6 ml of a 5 Nsodium hydroxide-methanol solution were added. Then, thepressure-resistant teflon cup was put in a pressure-resistant heatingcup made of SUS and, after securely sealing the cup, heating wasconducted at 100° C. for 15 hours.

Then the pressure-resistant heating cup after heating was cooled to roomtemperature, the pressure-resistant teflon cup that completely cooledwas removed and the contents in the cup were transferred to a 200 mlbeaker. Distilled water was added in the amount of up to about 150 ml.

After confirming that the contents had been completely dissolved, thesolution was neutralized with hydrochloric acid within a range of frompH 6.5 to 7.5. After the completion of the neutralization, the solutionwas diluted to 200 ml with distilled water and then the diluted solutionwas further diluted ten times with distilled water and the resultingsolution was taken as a sample solution.

Using this sample solution and an isophthalic acid standard solution,the measurement was conducted under the following conditions by ahigh-performance liquid chromatograph (HPLC) apparatus. As theisophthalic acid standard solution, those prepared by dissolving anisophthalic acid reagent manufactured by Tokyo Kasei Kogyo Co., Ltd.with distilled water were used.

Instrument: Waters HPLC LC-module 1

Column: Inertsil ODS-2 manufactured by GL Co., 5 μm (4.6×250)

Column temperature: 23±2° C.

Pump temperature: 23±2° C.

Eluent: 0.1% phosphoric acid/acetonitrile=80/20

Flow rate: 0.5 ml/min.

Run time: 50 minutes

Amount to be poured: 50 μl

Detection: UV-210 nm

Then, a calibration curve was made by a plot of the peak area ofisophthalic acid obtained from the standard solution as X-axis versusthe concentration as Y-axis. Using the resulting calibration curve, theconcentration of isophthalic acid (μg/ml) in the sample solution wascalculated.

The content of the IPA unit (% by weight) in the crystalline aromaticpolyester resin was calculated from the above concentration by using thefollowing equation:${{Content}\quad {of}\quad {IPA}\quad {unit}\quad \left( {\% \quad {by}\quad {weight}} \right)} = {\frac{\begin{matrix}\left\{ {{Concentration}\quad {of}} \right. \\{{isophthalic}\quad {acid}\quad \left( {\mu \quad g\text{/}{ml}} \right)}\end{matrix}}{\left\{ {{Weight}\quad {of}\quad {sample}\quad ({mg})} \right\}} \times 159.05}$

Measurement of content of CHDM Unit

After weighing about 100 mg of a sample in a pressure-resistant tefloncup, 10 ml of dimethyl sulfoxide for absorption spectrochemical analysismanufactured by Wako Pure Chemical Industries, Ltd. and 6 ml of a 5 Nsodium hydroxide-methanol solution were added. Then, thepressure-resistant teflon cup was put in a pressure-resistant heatingcup made of SUS and, after securely sealing the cup, heating wasconducted at 100° C. for 15 hours.

Then the pressure-resistant heating cup after heating was cooled to roomtemperature, the pressure-resistant teflon cup that completely cooledwas removed and the contents in the cup were transferred to a 100 mlbeaker. Guaranteed reagent methanol was added in the amount of up toabout 70 ml.

After confirming that the contents had been completely dissolved, thesolution was neutralized with hydrochloric acid within a range of frompH 6.5 to 7.5. After the completion of the neutralization, the solutionwas diluted to 100 ml with guaranteed reagent acetone and then thediluted solution was further diluted ten times with guaranteed reagentacetone and the resulting solution was taken as a sample solution.

This sample solution and a 1,4-cyclohexanedimethanol standard solutionwere weighed separately in a 10 ml centrifuge tube. After the solventwas evaporated to dryness with centrifuging, 0.2 ml of a TMS agentmanufactured by Tokyo Kasei Kogyo Co, Ltd. was added and heating wasconducted at 60° C. for 1 hour.

Using a gas chromatograph (GC) apparatus, the liquid after heating wasmeasured under the following conditions.

Instrument: Perkin Elmer GC AutoSystem

Column: DB-5 (0.25 mmφ×30 m×0.25 μm)

Oven temperature: 100° C. (2 minutes) R1−200° C.−R2−320° C. (5 minutes)

Heating rate: R1=10° C./min., R2=40° C./min.

Run time: 20 minutes

Injection temperature: 300° C.

Detector: FID (300° C.)

Gas pressure: 18 psi

Then, a calibration curve was made by a plot of the peak area of1,4-cyclohexanedimethanol obtained from the standard solution as X-axisversus the concentration as Y-axis. Using the resulting calibrationcurve, the concentration of 1,4-cyclohexanedimethanol (μg/ml) in thesample solution was calculated.

The content of the CHDM unit (% by weight) in the crystalline aromaticpolyester resin was calculated from the above concentration by using thefollowing equation:${{Content}\quad {of}\quad {CHDM}\quad {unit}\quad \left( {\% \quad {by}\quad {weight}} \right)} = {\frac{\begin{matrix}\left\{ {{Concentration}\quad {of}} \right. \\\left. {1,4\text{-cyclohexanedimethanol}\quad \left( {\mu \quad g\text{/}{ml}} \right)} \right\}\end{matrix}}{\left\{ {{Weight}\quad {of}\quad {sample}\quad ({mg})} \right\}} \times 98.62}$

The bulk density of the prepuffs and the apparent density of the moldedfoam article were measured by the following procedures.

Measurement of Bulk Density and Apparent Density

In accordance with the procedure defined in the Japanese IndustrialStandard No. JIS K6767₋₁₉₇₆ “Testing Method for Polyethylene Foams”, thebulk density of the prepuffs (g/cm³) and the apparent density of themolded foam article (g/cm³) were determined by using the followingequations respectively.${{Bulk}\quad {density}\quad {of}\quad {prepuffs}\quad \left( {g\text{/}{cm}^{3}} \right)} = \frac{\left\{ {{Weight}\quad {of}\quad {prepuffs}\quad (g)} \right\}}{\left\{ {{Bulk}\quad {volume}\quad {of}\quad {prepuffs}\quad \left( {cm}^{3} \right)} \right\}}$${{Apparent}\quad {density}\quad {of}\quad {molded}\quad {foam}\quad {article}\quad \left( {g\text{/}{cm}^{3}} \right)} = \frac{\left\{ {{Weight}\quad {of}\quad {molded}\quad {foam}\quad {article}\quad (g)} \right\}}{\left\{ {{Volume}\quad {of}\quad {molded}\quad {foam}\quad {article}\quad \left( {cm}^{3} \right)} \right\}}$

The open cell ratio of the prepuffs was measured by the followingprocedures.

Measurement of Open Cell Ratio

The open cell ratio (%) of the prepuffs was determined by conducting thefollowing tests (1) to (3).

(1) Measurement of weight and volume of prepuffs

The weight of prepuffs which can be charged in a sample cup of an aircomparison type specific gravimeter (Model 1000, manufactured by TokyoScience Co.) in the volume of about 80% was previously measured {weightA of prepuffs (g)}. The prepuffs were charged in the cup and the cup wasset to the specific gravimeter, and then the volume was measured by the1-1/2-1 atmosphere method {volume B of prepuffs (g/cm³)}.

(2) Measurement of apparent volume of prepuffs

In the state where a measuring dish of an electronical balance (HB3000,manufactured by YAMATO SCALE Co., Ltd.) was removed and a container madeof a wire gauze was suspended by a fitting, the above container wasdipped in water and the weight of the container was measured in water{weight C of container in water (g)}.

Then, the total amount of the prepuffs measured in the above item (1)was charged in the same container and the total weight of the containerand prepuffs was measured in the state of being dipped in water in thesame manner as described above {total weight D in water (g)}.

Then, the apparent volume E of the prepuffs (g/cm³) was determined bythe following equation:

 E=A+(C−D)

With the proviso that 1 g of water was reduced to the volume of 1 cm³.

(3) Open cell ratio

The open cell ratio (%) was determined from the results of the aboveitems (1) and (2) by the following equation:

Open cell ratio (%)=(E−B)×100/E

The fusion ratio of the molded foam article was measured by thefollowing procedures and, at the same time, the dimensional stabilityand appearance were evaluated by the following procedures.

Measurement of Fusion Ratio

After the molded foam article was fractured by folding in the thicknessdirection, the number of all prepuffs existing on the fractured surfaceand that of prepuffs wherein material fracture occurred were counted.Then, its fusion ratio (%) as an indication of the fusion between theprepuffs was determined by the following equation:${{Fusion}\quad {ratio}\quad (\%)} = {\frac{\begin{matrix}\left( {{Number}\quad {of}\quad {prepuffs}\quad {wherein}\quad {material}} \right. \\\left. {{fracture}\quad {occurred}} \right)\end{matrix}}{\begin{matrix}\left( {{Number}\quad {of}\quad {all}\quad {prepuffs}\quad {existing}\quad {on}} \right. \\\left. {{fractures}\quad {surface}} \right)\end{matrix}} \times 100}$

Evaluation of Dimensional Stability of Molded Foam Article

The shrinkage ratio of the molded foam article (%) on removal from themolds was determined from the distance L₁ corresponding to the maximumlength of the molded foam article of the molding cavity and the maximumlength L₂ of the molded foam article on removal from the molds by thefollowing equation. The sample where the shrinkage ratio was not morethan 2% was rated “∘” (good dimensional stability), while the samplewhere the shrinkage ratio was exceeded 2% was rated “X” (poordimensional stability).

Shrinkage ratio of molded foam article (%)=(L ₁ −L ₂)×100/L ₁

Evaluation of Surface Finish of Molded Foam Article

The surface finish of the molded foam article was visually observed andthen the sample where melting, poor particle extension were recognizedwas rated “X” (poor surface finish), while the sample where these werenot recognized was rated “∘” (good surface finish).

Measurement of Bending Strength

Using test pieces in size of 50 mm×100 mm×13 mm made by cutting themolded foam article, the bending test was conducted under the followingconditions and the maximum bending strength (MPa) was determined.

Apparatus: Tensilon universal testing machine

Bending rate: 50 mm/min.

Tip dig: Pressure wedge 3.2 R

Support base: 3.2 R

Span distance: 50 mm

Evaluation of Heat Resistance

The heat resistance of the molded foam article was evaluated inaccordance with the Japanese Industrial Standard No. JIS K6767₋₁₉₇₆.That is, the molded foam article was put in a high-temperature bath at140° C. and heated for 24 hours. The thermal dimensional change ratio(%) was determined from an absolute value of a difference between thesize L₃ before heating and the size L₄ after heating by the followingequation. Then, the sample where the thermal dimensional change ratiowas not more than 2% was rated “∘” (good heat resistance), while thesample where the dimensional change ratio was exceeded 2% was rated “X”(poor heat resistance).

Thermal dimensional change ratio (%)=|L ₃ −L ₄|×100/L ₃

Evaluation of Sink of Molded Foam Article

A board-like molded foam article in size of about 300×400×20 mm wasmolded from prepuffs. The maximum dimension T₁ and the minimum dimensionT₂ in the direction of thickness of the molded foam article immediatelyafter taken out from the mold were measured. The sink (%) was determinedfrom the following equation:

Sink(%)=|T ₁ −T ₂|×100/T ₁

The sample where the sink was not more than 5% was rated “∘” (withoutsink), while the sink was exceeded 5% was rated “X” (with sink).

EXAMPLE 1

100 parts by weight of a crystalline aromatic polyester resin(Tg: 68°C.) synthesized by polycondensation reaction of ethyleneglycol andterephthalic acid, 0.30 parts by weight of pyromellitic dianhydride as amodifier, and 0.03 parts by weight of sodium carbonate as an auxiliarymodifier were charged in an extruder (extruder bore: 65 mm, L/D ratio:35) and mixed and melted at a screw revolution 50 rpm and a barreltemperature in the range of from of 270 to 290° C. Then 1.0 parts byweight relative to the mixture of butane (n-butane/isobutane=7/3) asablowing agent was injected into the extruder barrel.

Then, the mixture in the molten state was extruded and foamed througheach nozzles of a multi nozzle die (15 nozzles having a diameter of 0.8mm are disposed on a line) connected to the tip portion of the extruderbarrel, and then cooled in a cooling water bath.

The cooled strand-like foam (foamed extrudate) was sufficientlydehydrated and then cut into generally cylindrical pieces using apelletizer to produce prepuffs.

The bulk density of the prepuffs was 0.13 g/cm³, the particle diameterwas from 1.4 to 2.5 mm, the crystallinity was 9.0%, the crystallizationpeak temperature was 126.0° C.

A mold cavity having an inner size of 300 mm×400 mm×20 mm, which wasformed by closing male and female mold members, was filled with theprepuffs. Then steam valve of the female mold member was opened whiledrain valve of the male mold member was opened to introduce steam intothe mold cavity at gauge pressure of 0.02 MPa for 15 seconds from thefemale mold member, after which steam valve of the male mold member wasopened while drain valve of the female mold member was opened tointroduce steam into the mold cavity at gauge pressure of 0.02 MPa for15 seconds from the male mold member, thus air in the mold cavity wasremoved.

Then, the steam valves of both the male and female mold members wereopened while the drain valves were closed to mold (expand and fuse)prepuffs by introducing steam into the mold cavity at gauge pressure of0.07 MPa for 15 seconds. The surface temperature of the mold at thistime was 116° C.

Then the steam valves and drain valves were all closed to cool themolded foam article naturally in the mold cavity for 120 seconds. Whenthat cooling was terminated, the surface temperature of the mold was101° C.

Then, the molded foam article was cooled finally by filling water fromcooling water nozzles of both the male and female mold members. Uponconfirming that the surface temperature of the mold was decreased to 50°C., the mold was opened to take out the molded foam article.

It was confirmed that the apparent density of the resulting molded foamarticle was 0.13 g/cm³ and the crystallinity was 30%. No sink was found.Its fusion ratio was 35% showing enough fusion to be normally used andthe surface finish was also good. Its shrinkage ratio of the molded foamarticle was 0.6% and thus the dimensional stability was good. Itsthermal dimensional change ratio was 0.92% and good heat resistance wasexhibited. Its bending strength was 0.72 MPa.

EXAMPLE 2

In the same manner as in Example 1, except that the gauge pressure ofthe steam to be introduced into the mold cavity on cavity-molding wasset at 0.1 MPa, a molded foam article was obtained. The surfacetemperature of the mold on cavity-molding was 122° C. and the surfacetemperature thereof was 105° C. at the time when the natural-cooling wasterminated.

It was confirmed that the apparent density of the resulting molded foamarticle was 0.13 g/cm³ and the crystallinity was 31%. No sink was found.Its fusion ratio was 35% showing enough fusion to be normally used andthe surface finish was also good. Its shrinkage ratio of the molded foamarticle was 0.6% and thus the dimensional stability was good. Itsthermal dimensional change ratio was 0.90% and good heat resistance wasexhibited. Its bending strength was 0.70 MPa.

EXAMPLE 3

In the same manner as in Example 1, except that 100 parts by weight of acrystalline aromatic polyester resin(IPA Unit: 1.4 parts by weight (%),Tg: 68.9° C.) synthesized by polycondensation reaction of ethyleneglycol, isophthalic acid and terephthalic acid was used, prepuffs wereproduced.

The bulk density of the prepuffs was 0.12 g/cm³, the particle diameterwas 1.4 to 2.5 mm, the crystallinity was 3.6% and the crystallizationpeak temperature was 135.0° C.

In the same manner as in Example 1, except that the cavity-moldingperiod was set for 50 seconds, the above produced prepuffs was used toobtain a molded foam article.

It was confirmed that the apparent density of the resulting molded foamarticle was 0.11 g/cm³ and the crystallinity was 24%. No sink was found.Its fusion ratio was 85% showing excellent fusion and the surface finishwas also good. Its shrinkage ratio of the molded foam article was 0.8%and thus the dimensional stability was good. Its thermal dimensionalchange ratio was 0.53% and good heat resistance was exhibited. Itsbending strength was 1.34 MPa.

EXAMPLE 4

In the same manner as in Example 3, except that the gauge pressure ofthe steam on cavity-molding was set at 0.1 MPa and the cavity-moldingperiod was set for 15 seconds, a molded foam article was obtained. Thesurface temperature of the mold on cavity-molding was 122° C. and thesurface temperature thereof was 106° C. at the time when thenatural-cooling was terminated.

It was confirmed that the apparent density of the resulting molded foamarticle was 0.11 g/cm³ and the crystallinity was 25%. No sink was found.Its fusion ratio was 85% showing excellent fusion and the surface finishwas also good. Its shrinkage ratio of the molded foam article was 1.0%and thus the dimensional stability was good. Its thermal dimensionalchange ratio was 0.51% and good heat resistance was exhibited. Itsbending strength was 1.33 MPa.

EXAMPLE 5

In the same manner as in Example 3, except that the gauge pressure ofthe steam on cavity-molding was set at 0.07 MPa, the cavity-moldingperiod was set for 15 seconds, and the period for cooling the moldnaturally after cavity-molding was set for 600 seconds, a molded foamarticle was obtained. The surface temperature of the mold oncavity-molding was 116° C. and the surface temperature thereof was 80°C. at the time when the natural-cooling was terminated.

It was confirmed that the apparent density of the resulting molded foamarticle was 0.11 g/cm³ and the crystallinity was 28%. No sink was found.Its fusion ratio was 85% showing excellent fusion and the surface finishwas also good. Its shrinkage ratio of the molded foam article was 0.5%and thus the dimensional stability was good. Its thermal dimensionalchange ratio was 0.49% and good heat resistance was exhibited. Itsbending strength was 1.34 MPa.

EXAMPLE 6

In the same manner as in Example 5, except that the gauge pressure ofthe steam on cavity-molding was set at 0.02 MPa and the cavity-moldingperiod was set for 50 seconds, a molded foam article was obtained. Thesurface temperature of the mold on cavity-molding was 106° C. and thesurface temperature thereof was 75° C. at the time when thenatural-cooling was terminated.

It was confirmed that the apparent density of the resulting molded foamarticle was 0.11 g/cm³ and the crystallinity was 24%. No sink was found.Its fusion ratio was 80% showing excellent fusion and the surface finishwas also good. Its shrinkage ratio of the molded foam article was 0.6%and thus the dimensional stability was good. Its thermal dimensionalchange ratio was 0.54% and good heat resistance was exhibited. Itsbending strength was 1.32 MPa.

EXAMPLE 7

In the same manner as in Example 1, except that the mixture obtained bymixing the following first and second resins in a weight ratio of 75:25,melting, kneading and ester-interexchanging (IPA unit: 2.5% by weight)were used as the crystalline aromatic polyester resin, prepuffs wereproduced.

The first resin: synthesized by polycondensation reaction of ethyleneglycol, isophthalic acid and terephthalic acid (IPA unit: 1.4% byweight, Tg: 68.9° C.)

The second resin: synthesized by polycondensation reaction of ethyleneglycol, isophthalic acid and terephthalic acid (IPA unit: 5.8% byweight, Tg: 70.0° C.)

The bulk density of the prepuffs was 0.12 g/cm³, the particle diameterwas from 1.4 to 2.5 mm, the crystallinity was 4.0% and thecrystallization peak temperature was 138.9° C.

In the same manner as in Example 1, except that the gauge pressure ofthe steam on cavity-molding was set at 0.07 MPa at gauge pressure andthe cavity-molding period was set for 15 seconds, the above producedprepuffs was used to obtain a molded foam article.

It was confirmed that the apparent density of the resulting molded foamarticle was 0.11 g/cm³ and the crystallinity was 23%. No sink was found.Its fusion ratio was 90% showing excellent fusion and the surface finishwas also good. Its shrinkage ratio of the molded foam article was 0.8%and thus the dimensional stability was good. Its thermal dimensionalchange ratio was 0.54% and good heat resistance was exhibited. Itsbending strength was 1.32 MPa.

Comparative Example 1

In the same manner as in Example 1, except that the mold was notnaturally cooled after cavity-molding, a molded foam article wasobtained.

The apparent density of its resulting molded foam article was 0.13g/cm³, the crystallinity was 18%, and the amount of sink was small as1.0%; however, its fusion ratio was low as 15% showing poor fusion. Thesurface finish was good. Its shrinkage ratio of the molded foam articlewas 0.6%. Its thermal dimensional change ratio was large as 5.1% andthus heat resistance was poor. Its bending strength was 0.49 MPa.

Comparative Example 2

In the same manner as in Comparative Example 1, except that the gaugepressure of the steam on cavity-molding was set at 0.1 MPa and thecavity-molding period was set for 120 seconds, a molded foam article wasobtained.

The apparent density of the resulting molded foam article was 0.13g/cm³, the crystallinity was 27%, and no sink was found; however, itsfusion ratio was low as 20% showing poor fusion. The surface finish wasgood. Its shrinkage ratio of the molded foam article was 0.6%. Itsthermal dimensional change ratio was large as 2.5% and thus heatresistance was poor. Its bending strength was 0.52 MPa.

Comparative Example 3

In the same manner as in Example 3, except that the gauge pressure ofthe steam on cavity-molding was set at 0.12 MPa, the cavity-moldingperiod was set for 15 seconds, and the period for cooling naturally themold after cavity-molding was set for 60 seconds, a molded foam articlewas obtained. The surface temperature of the mold on cavity-molding was128° C. and the surface temperature thereof was 115° C. at the time whenthe natural-cooling was terminated.

The apparent density of the resulting molded foam article was 0.11g/cm³, the crystallinity was 27%, and no sink was found. Its fusionratio was 75%. However, the surface finish was poor with unevennessbecause of melt by heat. Its shrinkage ratio of the molded foam articlewas large as 2.6% and thus the dimensional stability was poor. Itsthermal dimensional change ratio was small as 0.52%. Its bendingstrength was 0.52 MPa.

Comparative Example 4

In the same manner as in Example 3, except that the gauge pressure ofthe steam on cavity-molding was set at 0.005 MPa, the cavity-moldingperiod was set for 50 seconds, and the period for cooling naturally themold after cavity-molding was set for 600 seconds, a molded foam articlewas obtained. The surface temperature of the mold on cavity-molding was100° C. and the surface temperature thereof was 64° C. at the time whenthe cooling was terminated.

The apparent density of the resulting molded foam article was 0.11g/cm³, the crystallinity was 18%, the amount of sink was small as 1.0%and its fusion ratio was 60%. However, the surface finish was poor withunevenness due to shortage of heat. Its shrinkage ratio of the moldedfoam article was 1.2%. Its thermal dimensional change ratio was large as3.1% and thus the heat resistance was poor. Its bending strength was1.22 MPa.

Comparative Example 5

In the same manner as in Example 3, except that the gauge pressure ofthe steam on cavity-molding was set at 0.07 MPa, the cavity-moldingperiod was set for 15 seconds, and the surface temperature of the moldwas cooled down to 65° C. by 15 seconds after cavity-molding, a moldedfoam article was obtained. The surface temperature of the mold oncavity-molding was 116° C.

The apparent density of the resulting molded foam article was 0.11g/cm³, the crystallinity was 7%, and the amount of sink was large as6.5%. Its fusion ratio was 80%. The surface finish was good. Itsshrinkage ratio of the molded foam article was 2.2% and thus thedimensional stability was poor. Its thermal dimensional change ratio waslarge as 10.2% and thus the heat resistance was poor. Its bendingstrength was 1.32 MPa.

Comparative Example 6

In the same manner as in Example 3, except that the gauge pressure ofthe steam on cavity-molding was set at 0.07 MPa, the cavity-moldingperiod was set for 15 seconds, and the natural-cooling process wasomitted, a molded foam article was obtained. The surface temperature ofthe mold on cavity-molding was 116° C.

The apparent density of the resulting molded foam article was 0.11g/cm³, the crystallinity was 5%, and the amount of sink was large as7.5%. Its fusion ratio was 80%. The surface finish was good. Itsshrinkage ratio of the molded foam article was large as 2.6% and thusthe dimensional stability was poor. Its thermal dimensional change ratiowas large as 12.6% and thus the heat resistance was poor. Its bendingstrength was 1.31 MPa.

The above results are summarized in Tables 1 to 3.

TABLE 1 Molding Cooling Surface Surface IPA Temperature Time TimeTemperature (%) of Mold (° C.) (Second) (Second) of Mold (° C.) Examples1 0 116 15 120 101 2 0 122 15 120 105 3 1.4 116 50 120 101 4 1.4 122 15120 106 5 1.4 116 15 600 80 6 1.4 106 50 600 75 7 2.5 116 15 150 99Comp. 1 0 116 15 — — Examples 2 0 122 120 — — 3 1.4 128 15 60 115 4 1.4100 50 600 64 5 1.4 116 15 15 65 6 1.4 116 15 — —

TABLE 2 Molded Foam Article Apparent Fusion Density Crystallinity RatioDimensional (g/cm³) (%) (%) stability Examples 1 0.13 30 35 ∘ 2 0.13 3135 ∘ 3 0.11 24 85 ∘ 4 0.11 25 85 ∘ 5 0.11 28 85 ∘ 6 0.11 24 80 ∘ 7 0.1123 90 ∘ Comp. 1 0.13 18 15 ∘ Examples 2 0.13 27 20 ∘ 3 0.11 27 75 x 40.11 18 60 ∘ 5 0.11 7 80 x 6 0.11 5 80 x

TABLE 3 Molded Foam Article Bending Heat Strength Surface Resistance(MPa) Sink Finish Examples 1 ∘ 0.72 ∘ ∘ 2 ∘ 0.70 ∘ ∘ 3 ∘ 1.34 ∘ ∘ 4 ∘1.33 ∘ ∘ 5 ∘ 1.34 ∘ ∘ 6 ∘ 1.32 ∘ ∘ 7 ∘ 1.52 ∘ ∘ Comp. 1 x 0.48 ∘ ∘Examples 2 x 0.52 ∘ ∘ 3 ∘ 1.30 ∘ x 4 x 1.22 ∘ x 5 x 1.32 x ∘ 6 x 1.31 x∘

EXAMPLE 8

In the same manner as in Example 3, except that all the steam valves andthe drain valves were closed after cavity-molding (expanding and fusing)to naturally cool the mold for 30 seconds and the the steam at the gaugepressure of 0.02 MPa was introduced into the mold cavity for 45 seconds,a molded foam article was obtained.

It was confirmed that the apparent density of the resulting molded foamarticle was 0.11 g/cm³ and the crystallinity was 24%. No sink was found.Its fusion ratio was 85% showing excellent fusion and the surface finishwas also good. Its shrinkage ratio of the molded foam article was 0.8%and thus the dimensional stability was good. Its thermal dimensionalchange ratio was 0.53% and good heat resistance was exhibited. Itsbending strength was 1.34 MPa. Re-heating made it possible to obtain themolded foam article of the same quality with the one obtained in Example3 in a short period of time.

EXAMPLE 9

In the same manner as in Example 6, except that all the steam valves andthe drain valves were closed after cavity-molding to naturally cool themold for 60 seconds and then the steam at the gauge pressure of 0.018MPa was introduced into the mold cavity for 60 seconds, a molded foamarticle was obtained.

It was confirmed that the apparent density of the resulting molded foamarticle was 0.11 g/cm³ and the crystallinity was 24%. No sink was found.Its fusion ratio was 80% showing excellent fusion and the surface finishwas also good. Its shrinkage ratio of the molded foam article was 0.8%and thus the dimensional stability was good. Its thermal dimensionalchange ratio was 0.54% and good heat resistance was exhibited. Itsbending strength was 1.32 MPa. Re-heating made it possible to obtain themolded foam article of the same quality with the one obtained in Example6 in a short period of time.

EXAMPLE 10

In the same manner as in Example 7, except that all the steam valves andthe drain valves were closed after cavity-molding to naturally cool themold for 30 seconds and then the steam at the gauge pressure of 0.02 MPawas introduced into the mold cavity for 90 seconds, a molded foamarticle was obtained.

It was confirmed that the apparent density of the resulting molded foamarticle was 0.11 g/cm³ and the crystallinity was 24%. No sink was found.Its fusion ratio was 90% showing excellent fusion and the surface finishwas also good. Its shrinkage ratio of the molded foam article was 0.8%and thus the dimensional stability was good. Its thermal dimensionalchange ratio was 0.52% and good heat resistance was exhibited. Itsbending strength was 1.38 MPa. Re-heating made it possible to obtain themolded foam article of the same quality with the one obtained in Example6 in a short period of time.

EXAMPLE 11

In the same manner as in Example 7, except that 100 parts by weight ofonly the second resin was used as a crystalline aromatic polyesterresin, prepuffs were produced.

The above produced prepuffs was used at the gauge pressure of the steamof 0.07 MPa for 15 seconds for cavity-molding, and after the completionof cavity-molding, all the steam valves and the drain valves were closedto cool naturally the mold for 60 seconds. Thereafter, the steam of 0.02MPa at gauge pressure was introduced into the mold cavity for 30 secondsfor heating again (re-heating) to obtain a molded foam article.

It was confirmed that the apparent density of the resulting molded foamarticle was 0.11 g/cm³ and the crystallinity was 24%. No sink was found.Its fusion ratio was 95% showing excellent fusion and the surface wasalso good. Its shrinkage ratio of the molded foam article was 0.8% andthus the dimensional stability was good. Its thermal dimensional changeratio was 0.51% and good heat resistance was exhibited. Its bendingstrength was 1.46 MPa. Re-heating made is possible to obtain a moldedfoam article with good heat resistance and good surface finish in ashort period of time.

The above results are summarized in Tables 4 to 6.

TABLE 4 Molding Cooling Re-heating Surface Surface Surface IPATemperature Time Time Temperature Temperature Time (%) of Mold (° C.)(Second) (Second) of Mold (° C.) of Mold (° C.) (Second) Examples  8 1.4116 50 30 105 106 45  9 1.4 106 50 60 96 105 60 10 2.5 116 50 30 105 10690 11 5.8 116 15 60 103 106 30

TABLE 5 Molded Foam Article Apparent Fusion Density Crystallinity RatioDimensional (g/cm³) (%) (%) stability Examples  8 0.11 24 85 ∘  9 0.1124 80 ∘ 10 0.11 24 90 ∘ 11 0.11 24 95 ∘

TABLE 6 Molded Foam Article Bending Heat Strength Surface Resistance(MPa) Sink Finish Examples  8 ∘ 1.34 ∘ ∘  9 ∘ 1.32 ∘ ∘ 10 ∘ 1.38 ∘ ∘ 11∘ 1.46 ∘ ∘

EXAMPLE 12

In the same manner as in Example 3, except that the gauge pressure ofthe steam on cavity-molding (expanding and fusing) was set at 0.02 MPa,the cavity-molding period was set for 15 seconds and that the mold wascooled naturally for 120 seconds after cavity-molding, a molded foamarticle was obtained. The surface temperature of the mold oncavity-molding was 106° C.

The apparent density of the resulting molded foam article was 0.11g/cm³, the crystallinity was 16%, and the amount of sink was small as2.0%. Its fusion ratio was 60% showing good fusion and the surfacefinish was also good. Its shrinkage ratio of the molded foam article wassmall as 0.7% and thus the dimensional stability was good. Its bendingstrength was 1.46 MPa.

EXAMPLE 13

In the same manner as in Example 12, except that the cavity-moldingperiod was set for 50 seconds, a molded foam article was obtained. Thesurface temperature of the mold on cavity-molding was 106° C.

The apparent density of the resulting molded foam article was 0.11g/cm³, the crystallinity was 18%, and the amount of sink was small as1.0%. Its fusion ratio was 70% showing good fusion and the surfacefinish was also good. Its shrinkage ratio of the molded foam article wassmall as 0.8% and thus the dimensional stability was good. Its bendingstrength was 1.45 MPa.

EXAMPLE 14

In the same manner as in Example 12, except that the gauge pressure ofthe steam on cavity-molding was set at 0.07 MPa, the cavity-moldingperiod was set for 5 seconds and the mold was cooled naturally for 120seconds after cavity-molding, a molded foam article was obtained. Thesurface temperature of the mold on cavity-molding was 116° C., and thesurface temperature thereof at the time when the natural-cooling wasterminated was 101° C.

The apparent density of the resulting molded foam article was 0.11g/cm³, the crystallinity was 18%, and the amount of sink was small as1.0%. Its fusion ratio was 70% showing good fusion and the surfacefinish was also good. Its shrinkage ratio of the molded foam article wassmall as 0.7% and thus the dimensional stability was good. Its bendingstrength was 1.45 MPa.

EXAMPLE 15

In the same manner as in Example 12, except that the gauge pressure ofthe steam on cavity-molding was set at 0.07 MPa, the cavity-moldingperiod was set for 15 seconds and that the surface temperature of themold was cooled down to 112° C. in 30 seconds after cavity-molding, amolded foam article was obtained.

The apparent density of the resulting molded foam article was 0.11g/cm³, the crystallinity was 18%, and the amount of sink was small as1.0%. Its fusion ratio was 85% showing good fusion and the surfacefinish was also good. Its shrinkage ratio of the molded foam article wassmall as 0.7% and thus the dimensional stability was good. Its bendingstrength was 1.48 MPa.

EXAMPLE 16

In the same manner as in Example 12, except that the gauge pressure ofthe steam on cavity-molding was set at 0.07 MPa, the cavity-moldingperiod was set for 15 seconds and that the surface temperature of themold was cooled down to 80° C. in 30 seconds after cavity-molding, amolded foam article was obtained.

The apparent density of the resulting molded foam article was 0.11g/cm³, the crystallinity was 1%, and the amount of sink was small as3.0%. Its fusion ratio was 80% showing good fusion and the surfacefinish was also good. Its shrinkage ratio of the molded foam article wassmall as 1.0% and thus the dimensional stability was good. Its bendingstrength was 1.50 MPa.

EXAMPLE 17

In the same manner as in Example 12, except that the gauge pressure ofthe steam on cavity-molding was set at 1.0 MPa, the cavity-moldingperiod was set for 15 seconds and that the surface temperature of themold was cooled down to 120° C. in 30 seconds after cavity-molding, amolded foam article was obtained.

The apparent density of the resulting molded foam article was 0.11g/cm³, the crystallinity was 18%, and the amount of sink was small as1.0%. Its fusion ratio was 80% showing good fusion and the surfacefinish was also good. Its shrinkage ratio of the molded foam article wassmall as 0.8% and thus the dimensional stability was good. Its bendingstrength was 1.47 MPa.

EXAMPLE 18

The prepuffs produced in Example 7 were used under the gauge pressure ofthe steam of 0.07 MPa for 50 seconds for cavity-molding, and after thecompletion of cavity-molding, the mold was cooled naturally for 120seconds to obtain a molded foam article. The surface temperature of themold on cavity-molding was 116° C. and the surface temperature thereofat the time when the natural-cooling was terminated was 101° C.

It was confirmed that the apparent density of the resulting molded foamarticle was 0.11 g/cm³, the crystallinity was 17%, and the sink wassmall as 1.0%. Its fusion ratio was 90% showing excellent fusion and thesurface finish was also good. Its shrinkage ratio of the molded foamarticle was small as 0.8% and thus the dimensional stability was good.Its bending strength was 1.56 MPa.

The above results are summarized in Tables 7 to 9.

TABLE 7 Molding Cooling Surface Surface IPA Temperature Time TimeTemperature (%) of Mold (° C.) (Second) (Second) of Mold (° C.) Examples12 1.4 106 15 120 96 13 1.4 106 50 120 96 14 1.4 116 5 120 101 15 1.4116 15 30 112 16 1.4 116 15 30 80 17 1.4 122 15 30 120 18 2.5 116 50 120101

TABLE 8 Molded Foam Article Apparent Fusion Density Crystallinity RatioDimensional (g/cm³) (%) (%) stability Examples 12 0.11 16 60 ∘ 13 0.1118 70 ∘ 14 0.11 18 70 ∘ 15 0.11 18 85 ∘ 16 0.11 14 80 ∘ 17 0.11 18 80 ∘18 0.11 17 90 ∘

TABLE 9 Molded Foam Article Bending Strength Surface (MPa) Sink FinishExamples 12 1.46 ∘ ∘ 13 1.45 ∘ ∘ 14 1.45 ∘ ∘ 15 1.48 ∘ ∘ 16 1.50 ∘ ∘ 171.47 ∘ ∘ 18 1.56 ∘ ∘

EXAMPLE 19

100 parts by weight of a crystalline aromatic polyester resin(content ofIPA unit: 1.8% by weight, Tg: 68.9° C.) synthesized by polycondensationreaction of ethylene glycol, isophthalic acid and terephtalic acid, 0.30parts by weight of pyromellitic dianhydride as a modifier, 0.03 parts byweight of sodium carbonate as an auxiliary modifier and 0.01 parts byweight of a polytetraflouoroethylene resin as an expansion nucleatingagent were charged in an extruder (extruder bore: 65 mm, L/D ratio: 35)and mixed and melted at a screw revolution 50 rpm and a barreltemperature in the range of from of 270 to 290° C. Then 1.0 parts byweight relative to the mixture of butane (n-butane/isobutane=7/3) as ablowing agent was injected into the extruder barrel.

Then the mixture in th molten state was extruded and foamed at the shearspeed of 10438 sec⁻¹ (molten resin: 1.2 g/cm³) through each nozzle of amulti nozzle die (15 nozzles having a diameter of 0.8 mm are disposed ona line) connected to the tip portion of the extruder barrel, and thencooled in a cooling water bath.

The cooled strand-like foam (foamed extrudate) was sufficientlydehydrated and then cut into generally cylindrical pieces using apelletizer to produce prepuffs (primary prepuffs).

The bulk density of the primary prepuffs was 0.140 g/cm³, the averageparticle diameter was from 1.0 to 1.5 mm, the crystallinity was 4.5%,the open cell ratio was 17.0% and the crystallization peak temperaturewas 135.4° C.

The primary prepuffs were charged in a sealed container and thenimpregnated for 12 hours under the condition of temperature of 23° C.±2°C. after injecting a mixed inorganic gas with nitrogen and oxygen(content of nitrogen: 60% of volume) under gauge pressure of 0.5 MPa.Then, the primary prepuffs were taken out from the sealed container andre-expanded by heating with steam/air mixture-heating media(mixed volumeratio 10:90) at the temperature of 68° C. for 10 minutes using apre-expander equipped with a stirring blade to obtain secondaryprepuffs.

It was confirmed that the bulk density of the secondary prepuffs was0.058 g/cm³, open cell ratio was 17.0% and the crystallinity was 5.8%.

Then, the above secondary prepuffs was maturated at the temperature of23° C.±2° C. under normal pressure for 7 days, after which re-expansionratio was measured by steam foaming to find that it was expanded 1.6times and determined maturation was accomplished.

In the same manner as in Example 1, except that the secondary prepuffswere used, a molded foam article was obtained. The surface temperatureof the mold on cavity-molding was 116° C. and the surface temperaturethereof at the time when the natural cooling was terminated was 102° C.

It was confirmed that the apparent density of the resulting molded foamarticle was 0.058 g/cm³ and the crystallinity was 23%. No sink wasfound. Its fusion ratio was 80% showing high fusion and the surfacefinish was also good. Its shrinkage ratio of the molded foam article was0.6% and thus the dimensional stability was good. Its thermaldimensional change ratio was 0.58% and good heat resistance wasexhibited. Its bending strength was 0.82 MPa.

EXAMPLE 20

In the same manner as in Example 19, except that air was used as theinorganic gas to be impregnated into the primary prepuffs. Secondaryprepuffs were produced to obtain a molded foam article.

It was confirmed that the bulk density of the secondary prepuffs was0.060 g/cm³, open cell ratio was 16.0% and the crystallinity was 5.9%.

The apparent density of the resulting molded foam article was 0.060g/cm³ and the crystallinity was 23%. No sink was found. Its fusion ratiowas 80% showing high fusion and the surface finish was also good. Itsshrinkage ratio of the molded foam article was 0.6% and thus thedimensional stability was good. Its thermal dimensional change ratio was0.57% and good heat resistance was exhibited. Its bending strength was0.83 MPa.

EXAMPLE 21

In the same manner as in Example 19, except that 100% nitrogen gas wasused as the inorganic gas to be impregnated into the primary prepuffs.Secondary prepuffs were produced to obtain a molded foam article.

It was confirmed that the bulk density of the secondary prepuffs was0.060 g/cm³, open cell ratio was 16.5% and the crystallinity was 5.7%.

The apparent density of the resulting molded foam article was 0.060g/cm³ and the crystallinity was 23%. No sink was found. Its fusion ratiowas 80% showing high fusion and the surface finish was also good. Itsshrinkage ratio of the molded foam article was 0.6% and thus thedimensional stability was good. Its thermal dimensional change ratio was0.58% and good heat resistance was exhibited. Its bending strength was0.83 MPa.

EXAMPLE 22

In the same manner as in Example 20, except that the pressure onimpregnating with the inorganic gas was set at 1.0 MPa at gaugepressure, secondary prepuffs were produced to obtain a molded foamarticle.

It was confirmed that the bulk density of the secondary prepuffs was0.038 g/cm³, open cell ratio was 18.5% and the crystallinity was 6.2%.

The apparent density of the resulting molded foam article was 0.038g/cm³ and the crystallinity was 25%. No sink was found. Its fusion ratiowas 75% showing high fusion and the surface finish was also good. Itsshrinkage ratio of the molded foam article was 1.2% and thus thedimensional stability was good. Its thermal dimensional change ratio was0.60% and good heat resistance was exhibited. Its bending strength was0.54 MPa.

EXAMPLE 23

In the same manner as in Example 20, except that the pressure onimpregnating with the inorganic gas was set at 3.0 MPa at gaugepressure, secondary prepuffs were produced to obtain a molded foamarticle.

It was confirmed that the bulk density of the secondary prepuffs was0.030 g/cm³, open cell ratio was 20.0% and the crystallinity was 6.8%.

The apparent density of the resulting molded foam article was 0.030g/cm³ and the crystallinity was 26%. No sink was found. Its fusion ratiowas 70% showing high fusion and the surface finish was also good. Itsshrinkage ratio of the molded foam article was 1.4% and thus thedimensional stability was good. Its thermal dimensional change ratio was0.59% and good heat resistance was exhibited. Its bending strength was0.51 MPa.

EXAMPLE 24

In the same manner as in Example 20, except that the heating temperatureat re-expanding was set at 57° C., secondary prepuffs were produced toobtain a molded foam article.

It was confirmed that the bulk density of the secondary prepuffs was0.063 g/cm³, open cell ratio was 16.0% and the crystallinity was 4.4%.

The apparent density of the resulting molded foam article was 0.063g/cm³ and the crystallinity was 23%. No sink was found. Its fusion ratiowas 80% showing high fusion and the surface finish was also good. Itsshrinkage ratio of the molded foam article was 0.7% and thus thedimensional stability was good. Its thermal dimensional change ratio was0.57% and good heat resistance was exhibited. Its bending strength was0.84 MPa.

EXAMPLE 25

In the same manner as in Example 20, except that the heating temperatureat re-expanding was set at 88° C., secondary prepuffs were produced toobtain a molded foam article.

It was confirmed that the bulk density of the secondary prepuffs was0.061 g/cm³, open cell ratio was 16.5% and the crystallinity was 6.5%.

The apparent density of the resulting molded foam article was 0.061g/cm³ and the crystallinity was 24%. No sink was found. Its fusion ratiowas 80% showing high fusion and the surface finish was also good. Itsshrinkage ratio of the molded foam article was 0.6% and thus thedimensional stability was good. Its thermal dimensional change ratio was0.58% and good heat resistance was exhibited. Its bending strength was0.82 MPa.

EXAMPLE 26

In the same manner as in Example 20, except that the heating period atre-expanding was set for 5 minutes, secondary prepuffs were produced toobtain a molded foam article.

It was confirmed that the bulk density of the secondary prepuffs was0.061 g/cm³, open cell ratio was 16.0% and the crystallinity was 5.3%.

The apparent density of the resulting molded foam article was 0.061g/cm³ and the crystallinity was 23%. No sink was found. Its fusion ratiowas 80% showing high fusion and the surface finish was also good. Itsshrinkage ratio of the molded foam article was 0.6% and thus thedimensional stability was good. Its thermal dimensional change ratio was0.57% and good heat resistance was exhibited. Its bending strength was0.83 MPa.

EXAMPLE 27

In the same manner as in Example 20, except that the heating period atre-expanding was set for 2 minutes, secondary prepuffs were produced toobtain a molded foam article.

It was confirmed that the bulk density of the secondary prepuffs was0.061 g/cm³, open cell ratio was 15.0% and the crystallinity was 5.1%.

The apparent density of the resulting molded foam article was 0.061g/cm³ and the crystallinity was 23%. No sink was found. Its fusion ratiowas 80% showing high fusion and the surface finish was also good. Itsshrinkage ratio of the molded foam article was 0.6% and thus thedimensional stability was good. Its thermal dimensional change ratio was0.57% and good heat resistance was exhibited. Its bending strength was0.83 MPa.

The above results are summarized in the Tables 10 to 12.

TABLE 10 Pressure on Impregnating Gas Re-expanding Secondary PrepuffPressure Temperature Time Bulk Density Open Cell Crystallinity Gas (Mpa)(° C.) (Minute) (g/cm³) Ratio (%) (%) Examples 19 60% N₂ 0.5 68 10 0.05817.0 5.8 20 Air 0.5 68 10 0.060 16.0 5.9 21 100% N₂ 0.5 68 10 0.060 16.55.7 22 Air 1.0 68 10 0.038 18.5 6.2 23 Air 3.0 68 10 0.030 20.0 6.8 24Air 0.5 57 10 0.063 16.0 4.4 25 Air 0.5 88 10 0.061 16.5 6.5 26 Air 0.568 5 0.061 16.0 5.3 27 Air 0.5 68 2 0.061 16.0 5.1

TABLE 11 Molded Foam Article Apparent Fusion Density Crystallinity RatioDimensional (g/cm³) (%) (%) stability Examples 19 0.058 23 80 ∘ 20 0.06023 80 ∘ 21 0.060 23 80 ∘ 22 0.038 25 75 ∘ 23 0.030 26 70 ∘ 24 0.063 2380 ∘ 25 0.061 24 80 ∘ 26 0.061 23 80 ∘ 27 0.061 23 80 ∘

TABLE 12 Molded Foam Article Bending Heat Strength Surface Resistance(MPa) Sink Finish Examples 19 ∘ 0.82 ∘ ∘ 20 ∘ 0.83 ∘ ∘ 21 ∘ 0.83 ∘ ∘ 22∘ 0.54 ∘ ∘ 23 ∘ 0.51 ∘ ∘ 24 ∘ 0.84 ∘ ∘ 25 ∘ 0.82 ∘ ∘ 26 ∘ 0.83 ∘ ∘ 27 ∘0.83 ∘ ∘

EXAMPLE 28

In the same manner as in Example 1, except that the same primaryprepuffs as those produced in Example 19 were charged in a sealedcontainer and then a mixed inorganic gas with nitrogen and oxygen(content of nitrogen: 60% of volume) was injected therein at gaugepressure of 0.5 MPa to impregnate the primary prepuffs for 2 hours underthe condition of temperature of 20° C. and to fill the mold cavity withthe same for cavity-molding (expanding and fusing), a molded foamarticle was obtained. The surface temperature of the mold oncavity-molding was 116° C. and the surface temperature thereof was 102°C. at the time when the natural-cooling was terminated.

The apparent density of the resulting molded foam article was 0.14 g/cm³and the crystallinity was 14%. The sink was small as 3.0%. Its fusionratio was 70% showing high fusion and the surface finish was also good.Its shrinkage ratio of the molded foam article was 0.1% and thus thedimensional stability was especially good. Its bending strength was 1.46MPa.

EXAMPLE 29

In the same manner as in Example 28, except that air was used as theinorganic gas for the vapor phase impregnation, a molded foam articlewas obtained.

The apparent density of the resulting molded foam article was 0.14 g/cm³and the crystallinity was 14%. The sink was small as 3.0%. Its fusionratio was 70% showing high fusion and the surface finish was also good.Its shrinkage ratio of the molded foam article was 0.1% and thus thedimensional stability was especially good. Its bending strength was 1.47MPa.

EXAMPLE 30

In the same manner as in Example 28, except that carbon dioxide gas wasused as the inorganic gas for the vapor phase impregnation, a moldedfoam article was obtained.

The apparent density of the resulting molded foam article was 0.14 g/cm³and the crystallinity was 70%. The sink was small as 3.0%. Its fusionratio was 70% showing high fusion and the surface finish was also good.Its shrinkage ratio of the molded foam article was 0.1% and thus thedimensional stability was especially good. Its bending strength was 1.46MPa.

EXAMPLE 31

In the same manner as in Example 20, except that the produced secondaryprepuffs were charged in a sealed container and then a mixed inorganicgas with nitrogen and oxygen (content of nitrogen: 60% of volume) wasinjected therein at gauge pressure of 0.5 MPa to impregnate thesecondary prepuffs for 2 hours under the condition of temperature of 20°C., after which the mold cavity was filled with the same immediately, amolded foam article was obtained.

The apparent density of the resulting molded foam article was 0.058g/cm³ and the crystallinity was 18%. The sink was small as 1.0%. Itsfusion ratio was 70% showing high fusion and the surface finish was alsogood. Its shrinkage ratio of the molded foam article was 0.2% and thusthe dimensional stability was especially good. Its bending strength was0.88 MPa.

EXAMPLE 32

In the same manner as in Example 31, except that air was used as theinorganic gas for the vapor phase impregnation, a molded foam articlewas obtained.

The apparent density of the resulting molded foam article was 0.058g/cm³ and the crystallinity was 18%. The sink was small as 1.0%. Itsfusion ratio was 70% showing high fusion and the surface finish was alsogood. Its shrinkage ratio of the molded foam article was 0.2% and thusthe dimensional stability was especially good. Its bending strength was0.88 MPa.

EXAMPLE 33

In the same manner as in Example 31, except that carbon dioxide gas wasused as the inorganic gas for the vapor phase impregnation, a moldedfoam article was obtained.

The apparent density of the resulting molded foam article was 0.058g/cm³ and the crystallinity was 18%. The sink was small as 1.0%. Itsfusion ratio was 70% showing high fusion and the surface finish was alsogood. Its shrinkage ratio of the molded foam article was 0.2% and thusthe dimensional stability was especially good. Its bending strength was0.88 MPa.

EXAMPLE 34

In the same manner as in Example 32, except that the gauge pressure ofthe inorganic gas applied for the vapor phase impregnation was set at0.2 MPa, a molded foam article was obtained.

The apparent density of the resulting molded foam article was 0.058g/cm³ and the crystallinity was 19%. The sink was small as 0.5%. Itsfusion ratio was 75% showing high fusion and the surface finish was alsogood. Its shrinkage ratio of the molded foam article was 0.2% and thusthe dimensional stability was especially good. Its bending strength was0.86 MPa.

EXAMPLE 35

In the same manner as in Example 32, except that at gauge pressure ofthe inorganic gas applied for the vapor phase impregnation was set at2.0 MPa, a molded foam article was obtained.

The apparent density of the resulting molded foam article was 0.058g/cm³ and the crystallinity was 16%. The sink was small as 2.0%. Itsfusion ratio was 60% showing high fusion and the surface finish was alsogood. Its shrinkage ratio of the molded foam article was 0.2% and thushe dimensional stability was especially good. Its bending strength was0.87 MPa.

EXAMPLE 36

In the same manner as in Example 32, except that the gauge pressure ofthe inorganic gas applied for the vapor phase impregnation was set at0.05 MPa, a molded foam article was obtained.

The apparent density of the resulting molded foam article was 0.058g/cm³ and the crystallinity was 21%. No sink was found. Its fusion ratiowas 80% showing high fusion and the surface finish was also good. Itsshrinkage ratio of the molded foam article was 0.2% and thus thedimensional stability was especially good. Its bending strength was 0.87MPa.

The above results are summarized in Tables 13 to 15.

TABLE 13 Prepuff Bulk Vapor Phase Impregnation Density CrystallinityPressure Temperature Time (g/cm³) (%) Gas (Mpa) (° C.) (Hour) Examples28 0.14 4.5 60% N₂ 0.5 20 2 29 0.14 4.5 Air 0.5 20 2 30 0.14 4.5 Carbon0.5 20 2 Dioxide Gas 31 0.058 5.8 60% N₂ 0.5 20 2 32 0.058 5.8 Air 0.520 2 33 0.058 5.8 Carbon 0.5 20 2 Dioxide Gas 34 0.058 5.8 Air 0.2 20 235 0.058 5.8 Air 2.0 20 2 36 0.058 5.8 Air 0.05 20 2

TABLE 14 Molded Foam Article Apparent Fusion Density Crystallinity RatioDimensional (g/cm³) (%) (%) stability Examples 28 0.14 14 70 ⊚ 29 0.1414 70 ⊚ 30 0.14 14 70 ⊚ 31 0.058 18 70 ⊚ 32 0.058 18 70 ⊚ 33 0.058 18 70⊚ 34 0.058 19 75 ⊚ 35 0.058 16 60 ⊚ 36 0.058 21 80 ⊚

TABLE 15 Molded Foam Article Bending Strength Surface (MPa) Sink FinishExamples 28 1.46 ∘ ∘ 29 1.47 ∘ ∘ 30 1.46 ∘ ∘ 31 0.88 ∘ ∘ 32 0.88 ∘ ∘ 330.88 ∘ ∘ 34 0.86 ∘ ∘ 35 0.87 ∘ ∘ 36 0.87 ∘ ∘

What we claim is:
 1. A process for producing a crystalline aromaticpolyester resin molded foam article, which comprises molding crystallinearomatic polyester resin prepuffs using male and female mold members ofa mold assembly comprising the steps of: (1) filling a mold cavity,which is formed by closing the male and female mold members, with thecrystalline aromatic polyester resin prepuffs; (2) heating an interiorsurface of the mold to a temperature not less than (Tg+35) and nogreater than (Tg+57)°C. (Tg being a glass transition temperature of thecrystalline aromatic polyester resin prepuffs), thereby to mold thefilled prepuffs; (3) cooling the surface of the mold to a temperaturenot lower than Tg for a period of at least 20 seconds while holding themolded form article in the mold as it is; and (4) after step (3),cooling the surface of the mold lower than Tg.
 2. The process forproducing a crystalline aromatic polyester resin molded foam articleaccording to claim 1, wherein said heating is conducted using steam. 3.A process for producing a crystalline aromatic polyester resin moldedfoam article, which comprises molding crystalline aromatic polyesterresin prepuffs using male and female mold members of a mold assemblycomprising the steps of: (1) filling a mold cavity, which is formed byclosing the male and female mold members, with the crystalline aromaticpolyester resin prepuffs; (2) heating an interior surface of the mold toa temperature in a range of from (Tg+35) to (Tg+57)°C. (Tg being a glasstransition temperature of the crystalline aromatic polyester resinprepuffs), thereby to mold the filled prepuffs; (3) cooling the surfaceof the mold to a temperature not lower than Tg for a period of at least20 seconds while holding the molded form article in the mold as it is;and (4) removing the molded form article from the mold, after finallycooling the surface of the mold lower than Tg, wherein a step (3a) isadded between steps (3) and (4): (3a) heating the surface of the moldagain to the temperature within a range of from (Tg+20) to (Tg+57)°C.,accelerating crystallization of the molded foam.
 4. The process forproducing a crystalline aromatic polyester resin molded foam articleaccording to claim 2, wherein a step (3a) is added between steps (3) and(4): (3a) heating the surface of the mold again to the temperaturewithin a range of from (Tg+20) to (Tg+57)°C., acceleratingcrystallization of the molded foam.
 5. The process for producing acrystalline aromatic polyester resin molded foam article according toany one of claim 1, 2, 3, or 4, further comprising prior to step (1)impregnating the prepuffs with an inorganic gas at gauge pressure of0.01 to 5 MPa.
 6. The process for producing a crystalline aromaticpolyester resin molded foam article according to claim 5, wherein air isused as the inorganic gas.
 7. The process for producing a crystallinearomatic polyester resin molded foam article according to any one ofclaim 1, 2, 3, or 4, further comprising prior to step (1): re-expandingof the prepuffs at least one time by impregnating the prepuffs with agas at gauge pressure of 0.1 to 5 MPa at a temperature lower than Tg for1 to 24 hours and then expanding the prepuffs at a temperature of 55 to90° C. in 12 minutes or less.
 8. The process for producing a crystallinearomatic polyester resin molded foam article according to claim 7,wherein air is used as the gas.
 9. The process for producing acrystalline aromatic polyester resin molded foam article according toclaim 7, wherein steam is used as a heating medium for re-expanding. 10.The process for producing a crystalline aromatic polyester resin moldedfoam article according to claim 8, wherein steam is used as a heatingmedium for re-expanding.
 11. The process for producing a crystallinearomatic polyester resin molded foam article according to claim 7,wherein the re-expanded prepuffs are further subjected to impregnatingwith an inorganic gas at gauge pressure of 0.01 to 5 Mpa prior to step(1).
 12. The process for producing a crystalline aromatic polyesterresin molded foam article according to claim 8, wherein the re-expandedprepuffs are further subjected to impregnating with an inorganic gas atgauge pressure of 0.01 to 5 Mpa prior to step (1).
 13. The process forproducing a crystalline aromatic polyester resin molded foam articleaccording to claim 9, wherein the re-expanded prepuffs are furthersubjected to impregnating with an inorganic gas at gauge pressure of0.01 to 5 Mpa prior to step (1).
 14. The process for producing acrystalline aromatic polyester resin molded foam article according toclaim 10, wherein the re-expanded prepuffs are further subjected toimpregnating with an inorganic gas at gauge pressure of 0.01 to 5 Mpaprior to step (1).
 15. The process for producing a crystalline aromaticpolyester resin molded foam article according to claim 11, wherein airis used as the inorganic gas.
 16. The process for producing acrystalline aromatic polyester resin molded foam article according toclaim 12, wherein air is used as the inorganic gas.
 17. The process forproducing a crystalline aromatic polyester resin molded foam articleaccording to claim 13, wherein air is used as the inorganic gas.
 18. Theprocess for producing a crystalline aromatic polyester resin molded foamarticle according to claim 14, wherein air is used as the inorganic gas.